Vaccines have proven to be invaluable in the fight against infectious diseases. Yet in the case of AIDS several different approaches have so far failed to produce an effective vaccine. The evidence is convincing that a strong immune response to HIV can be effective in preventing HIV infection or at least limiting the progression to AIDS. In addition a better understanding has been gained as to the reasons why individuals succumb to HIV infection. This information, together with basic advances in our understanding of antigen presentation pathways and the use of molecular techniques applied to identifying immunogenic epitopes, should make it feasible to design an effective vaccine. DNA vaccines offer a number of advantages over the traditional methods, in particular the lack of pathogenesis, as well as the possibility to design into the DNA encoding the antigens both immunogenic epitopes and antigen presentation pathway signals. The goal of the proposal is to use a molecularly engineered antibody to target DNA, encoding an antigen, to dendritic cells in vivo. To test this concept, the rat monoclonal antibody, DEC-205, available from the ATCC, will be used; it binds to a mouse dendritic cell surface antigen, which is involved in antigen internalization. The cDNAs of the antibody will be cloned, and the heavy chain cDNA modified to contain a DNA binding domain. The cDNAs will then be transferred into a recombinant baculovirus so that a Fab fused with a DNA binding domain will be expressed and purified from insect cells. The Fab/DNA binding domain will be complexed with a plasmid encoding a reporter gene to test its ability to target specifically mouse dendritic cells in tissue culture. Subsequently, the Fab/DNA complex will be tested in vivo.